Justice Lewis F. Powell Jr. is still on the Supreme Court's injured reserve list after undergoing surgery Jan. 4 for removal of a cancerous prostate gland.

Originally, Powell had expected to be hospitalized for about two weeks, but his stay at Rochester Methodist Hospital lasted 25 days, followed by another week at a hotel.

Hospital officials said the longer stay was not a result of medical complications but because it took him longer than expected to recuperate.

Powell, 77, returned to Washington Wednesday and plans to work from his home.

Word is that while he is feeling all right, he may not have time to prepare adequately for oral arguments Feb. 19 and may not take the bench for them.

Powell still has the option of listening to arguments and voting in the two dozen cases the court heard while he was hospitalized.

But court watchers say he is unlikely to do so unless his vote would break a tie in an important case.

Powell's illness sparked rumors that he would be the first of five justices over age 76 to retire. But the latest word is that Powell, appointed by President Nixon in 1972, says he has no intention of shedding his robes. FILLING THE BENCH . . .

The musical chairs game at the White House is putting a temporary glitch in the Reagan administration's plan to fill vacant federal judgeships. At last count, more than 100 seats on federal trial and appellate courts were vacant, and numerous candidates yearned to be reviewed.

The nine-member White House review committee, chaired by White House counsel Fred F. Fielding, usually meets on Thursdays. It hasn't met in several weeks, however, in part because of scheduling conflicts and in part because it isn't clear who is to meet with whom.

The group used to include Attorney General William French Smith, three top Justice officials, Fielding, former chief of staff James A. Baker III, White House counselor Edwin Meese III, M.B. Oglesby, assistant to the president for legislative affairs and John S. Herrington, White House personnel chief. Baker and Herrington have moved on to new jobs. Donald T. Regan, the president's new chief of staff, who is not a lawyer, probably will fill Baker's committee slot and could be joined by another nonlawyer, White House political chief Edward J. Rollins. Regan's new congressional adviser, Max L. Friedersdorf, may join the group. Meese would stay on the committee no matter what happens to his nomination as attorney general. THE COST OF THE COURTS . . .

Left out for the moment in all the hoopla over President Reagan's budget proposals is the cost of running the federal court system. The requested budget for fiscal 1986 would top $1 billion for the first time -- $1,138,731,000 to be precise. That includes $17 million and change to run the Supreme Court. The high court's request is about $900,000 more than this year's budget. But the total request calls for a $160 million increase.

A good portion of the increase would cover the cost of 95 additional judges that Congress approved last year. Each judge with office, phone, secretary, clerks and so forth costs about $350,000.

Court officials hasten to point out that the judiciary still accounts for only one-tenth of 1 percent of the federal budget. More attention will be given the judiciary's expenses in March, when Justices Powell and Sandra Day O'Connor try to justify their budget on Capitol Hill.